Optical element and method for the production thereof

ABSTRACT

The invention relates to a method for producing an optical element, preferably a security feature, wherein a film having a first embossed hologram in an embossing layer is provided, and a second embossed hologram is embossed into the same embossing layer such that the first embossed hologram is partly replaced with the second embossed hologram. The invention further relates to a method for producing an optical element wherein an embossable film provided with an embossed hologram is partly filled with printing lacquer, and a method for producing an optical element wherein hologram embossing is prevented by prior partial printing of the embossing film with curable printing lacquer. The invention relates further to optical features producible by the inventive methods, documents of value having an inventive optical feature and a numbering embosser for use in an inventive production method.

[0001] This invention relates to methods for producing an opticalelement, optical elements producible by said methods, documents of valuehaving such optical elements and a numbering embosser for use in aninventive method.

[0002] Documents, certificates, bank notes, identity cards, plasticcards, etc., can be reproduced true-to-detail and colorfast using modernhigh-resolution color scanners and using color laser printers or thermalsublimation printers. The common availability of color copiers has alsomade it substantially easier to produce high-quality forgeries.

[0003] There is therefore a need to make documents, identity cards, banknotes, papers of value, plastic cards, etc., forgery-proof throughadditionally applied security features. Such security features can atleast make it much more difficult and expensive to produce ahigh-quality forgery. Known security features are watermarks, silkthreads, intertwined line structures, and the use of special paper. Theapplication of metalized embossed holograms to bank notes, credit cardsand Eurocheque cards has also become generally established. Due to theholographic effect, such embossed holograms can also be used for aspecial esthetic design of such documents or other objects.

[0004] Such embossed holograms are produced e.g. by embossingholographic image reliefs into an embossable film in bulk. An adhesivelayer is applied to the embossed film. Further design is therefore nolonger possible. With the adhesive layer the embossed film is appliede.g. as a security feature.

[0005] However, such simple embossed holograms likewise offer onlylimited protection from forgery. The increasing spread of correspondingtechnology already makes it possible to imitate such embossed holograms.

[0006] It would therefore be desirable if methods were available forproducing optical elements whose forgery is further impeded and thatpermit simple individualization. It is the problem of the presentinvention to specify corresponding methods for producing opticalelements, optical elements that are difficult to forge, documents ofvalue having such optical elements and an embossing tool for use in aproduction method.

[0007] This problem is solved with a method having the features of claim1, an optical element having the features of claim 23 and a numberingembosser having the features of claim 22.

[0008] In a first inventive method, an embossable film or substratesurface having a first embossed hologram is first provided. Saidembossed hologram can have been embossed into an embossable film as aholographic image relief in the known way. Thus, the first embossedhologram in the embossing layer of said film is mass-producible. In theinventive method a second embossed hologram is embossed into the sameembossing layer where the first embossed hologram is already formed.According to the invention, the second embossed hologram partly replacesthe first embossed hologram.

[0009] In the inventive method two embossed holograms are thus embossedinto one another. The second embossed hologram can be selected so thatit holographically reconstructs a different image from the firstembossed hologram when illuminated. When the second embossed hologram isviewed a different optical effect arises than when the surfaces bearingthe first embossed hologram are viewed. The optical structures, e.g.diffraction gratings of embossed holograms, have typical orders ofmagnitude and spacings of a few hundred nanometers and are thus notrecognizable with the naked eye. Only when illuminated withcorresponding reconstruction light and viewed at the holographicreconstruction angle does the holographically stored information becomevisible. Unlike e.g. two adhesive holograms that have been glued oneabove the other, the two embossed hologram structures present in oneembossing layer can thus normally not be recognized by simple viewingwith the naked eye. Only illumination with reconstruction light andviewing at the corresponding reconstruction angle make the doublestructure recognizable.

[0010] The inventive method can thus be used to produce an opticalelement that firstly causes a special optical, and possibly especiallyesthetic, effect. Additionally, the structure having a plurality ofdifferent embossed holograms in one embossing layer is more difficult toimitate. This results in a higher recognition value, which can also bechecked easily without special equipment.

[0011] Embossing the second embossed hologram structure into the sameembossing layer as the first embossed hologram structure permits simpleproduction. It is not necessary to glue different layers onto each otheror interconnect them.

[0012] Further embossing steps can of course be provided for furtherembossed holograms that partly replace the first and/or previouslyformed embossed holograms.

[0013] The second embossed hologram structure can have the same externalform for all optical elements. However, a significant increase inforgery-proofness and/or range of application is given if the secondembossed hologram is different for each optical element. In this way theoptical element can be individualized as a security feature, e.g. in theform of a consecutive registration number.

[0014] In advantageous embodiments, the first and second embossedholograms have different reconstruction angles and/or differentreconstruction wavelengths.

[0015] Additional information can be represented if the external form ofthe second embossed hologram can likewise convey information. The firstembossed hologram is then replaced with the second embossed hologram inthe form of the external form of the latter. Upon viewing of the opticalelement, the information stored in the first embossed hologram or theinformation stored in the second embossed hologram thus becomes visibledepending on the viewing angle or viewing light. It additionally becomesrecognizable what external form the second embossed hologram has. Forexample, the second embossed hologram can have the external form of anumber. This number can e.g. correspond to the serial number of adocument of value.

[0016] While the first embossed hologram can be formed in the embossinglayer of the film in bulk, the second embossed hologram can be embossedindividually for each single optical feature in the form of a differentnumber. This permits the optical features to be individualized verywell.

[0017] The inventive method can be carried out especially simply using anumbering embosser which advantageously comprises metallic positive ornegative numbers produced by etching or engraving technology and eachhaving a holographic relief applied thereto. If the numbers of thenumbering embosser already bear the holographic relief for the secondembossed hologram on the embossing surface, the numbering process forproducing the second embossed hologram can be performed as in acustomary numbering embossing process. While a first embossed hologramis being brought into the embossing position for the second embossedhologram, the numbering tool switches to the desired number. The secondembossed hologram is embossed into the embossing layer of the firstembossed hologram layer in the external form of the desired number.Subsequently, an adhesive layer is e.g. applied to the back and theoptical feature glued to the object to be protected, e.g. a document ofvalue. A further first embossed hologram is brought into the positionfor embossing the second embossed hologram while the numbering embosseradvances one number. The process is now repeated accordingly.

[0018] The holographic relief on the embossing surface of the numberingtool can be e.g. a corresponding nickel master bearing the embossedstructure of the second embossed hologram in metallic form.

[0019] In another advantageous embodiment, a nickel band having aholographic relief is placed over the number wheel of an embossednumbering unit. The embossing surfaces of the numbering unit then neednot be provided with the holographic relief themselves. In the embossingprocess for the second embossed hologram the embossing surface of theparticular number of the numbering embosser presses the nickel bandhaving the holographic relief into the embossing layer of the firstembossed hologram. In the external form of the particular number of thenumbering embosser the holographic relief structure of the nickel bandis thus embossed into the embossing layer of the first embossedhologram.

[0020] An inventive optical element that can be used in particularadvantageously as a security feature for documents of value comprises afirst embossed hologram in an embossing layer and a second embossedhologram in the same embossing layer. The second embossed hologram isdisposed within the external outlines of the first embossed hologram.

[0021] The problem is likewise solved with a method having the featuresof one of claims 11 and 13 and an optical element having the features ofone of claims 26 and 27.

[0022] In such an inventive method, an embossable film or substratesurface is printed partly with a curable printing lacquer. Subsequentlysaid lacquer is cured. In a further method step an embossed hologram isembossed onto the thus partly printed substrate, the cured lacquerpreventing embossing in the printed partial areas. Such an inventivemethod likewise permits the representation of information by theexternal form of the surface printed with the cured lacquer. The imagethat is reconstructed holographically when the embossed hologram isilluminated leaves out the printed partial areas. In this way theinformation represented e.g. in the external form of the printed areasis visible.

[0023] In a further inventive method, an embossable film or substratesurface having an embossed hologram is first provided. To said embossedhologram a printing lacquer is applied in partial areas to fill theembossed relief structure of the hologram. Optionally, the lacquer issubsequently cured. This inventive method thus also produces an opticalelement whose embossed hologram is left out in partial areas. Again, thepartial areas can have an external form of information, e.g. a number.Upon illumination of the embossed hologram, the filled partial areas donot reconstruct the image stored in the hologram, so that theinformation stored by the external form becomes recognizable.

[0024] In the latter inventive method, it is thus possible in a simpleway to represent additional information going beyond what isreconstructed holographically by the embossed hologram. Application ofthe printing lacquer is possible in a simple way and optionallyindividually for each single optical element. This guarantees highforgery-proofness.

[0025] In these inventive methods using printing lacquer, the externalform of the printed partial areas can again correspond to an individualnumber, thereby permitting e.g. a consecutive registration of opticalelements or the security features or documents of value providedtherewith.

[0026] The printing lacquer can be applied to the embossing film indifferent ways. Application is especially simple and reliable using ajet printer, similar to an ink jet printer, which applies the lacquer inthe desired external form. Application with a laser printer also permitssimple and reliable design.

[0027] It is especially advantageous if the printing lacquer istransparent or colored-transparent. Such an embodiment increases theforgery-proofness of the finished optical element since the surface inthe partial areas does not differ from the surrounding embossed hologramareas by a completely different color or transmission.

[0028] The optical element produced with an inventive method can be usedand fastened in different ways, e.g. as a security element. It isespecially simple and thus advantageous if an adhesive layer forfastening the optical element to the object to be protected is appliedto the unembossed side only after all embossing processes have beenperformed. An adhesive layer attached only after all embossing processeshave been performed does not hinder the embossing processes.

[0029] It is especially advantageous to use an adhesive coating in theform of a hot-melt adhesive coating which can be treated thermally.

[0030] In all inventive methods, a metalization or coating with a highlyrefractive material is advantageously performed at the end of theproduction process but at least only after all embossing processes, forprotecting the structure or making the holographic effect wellrepresentable.

[0031] For the inventive method one can use embossable substratesurfaces, in particular and especially advantageously hot stampingfoils, sticker embossing films, paper coated with thermal lacquer orsubstrate surfaces coated with UV lacquer.

[0032] An inventive optical element of another embodiment, which canlikewise be used in particular advantageously as a security feature fordocuments of value, comprises an embossed hologram in an embossinglayer, whereby at least one partial area of the relief embossed into theembossing layer is filled so that no holographic reconstruction can takeplace in the partial area.

[0033] In an inventive optical element of a further embodiment, whichcan likewise be used in particular advantageously as a security featurefor documents of value, an embossed hologram is provided in an embossinglayer, the relief being left out in the embossing layer at least in onepartial area.

[0034] It is especially advantageous to use the inventive methods andoptical elements in documents of value, e.g. as a security feature, asis the object of claims 28 and 29.

[0035] Hereinafter the invention will be explained in detail withreference to preferred embodiments and designs. The figures showexamples of inventive embodiments in a schematic representation, whereby

[0036]FIG. 1 shows an inventive document of value having an inventiveoptical feature,

[0037]FIG. 2 shows an inventive optical element,

[0038]FIG. 3 shows another embodiment of an inventive optical element,

[0039]FIG. 4 shows an embossing die of an inventive numbering embosser,

[0040]FIG. 5 shows the plan view of an inventive optical elementaccording to a further embodiment, and

[0041]FIG. 6 shows a cross section along line A-A in FIG. 5.

[0042]FIG. 1 shows a schematic representation of e.g. bank note 1. Saidbank note has applied thereto in known fashion information, e.g. thevalue and image information, which is of little interest here andaccordingly not included in the figure. Bank note 1 optionally containsvarious security features, such as watermarks or guilloches, which arelikewise omitted here.

[0043] Number 3 designates an inventive security feature on inventivebank note 1. Inventive security feature 3 includes, among other things,number 5, in the shown example the number “123.”

[0044]FIG. 2 shows the inventive security feature of this embodiment inan enlarged representation. It comprises first embossed hologram 30,which is shown only schematically in the form of lines. Said firstembossed hologram can be a diffraction grating. The spacing of theindividual grating stripes is typically a few hundred nanometers topermit interference effects of visible light to be produced in knownfashion. The invention is of course not limited to such stripe-shapedholograms, but can have any desired forms of embossed hologramrepresenting different information holographically, e.g. the image of athree-dimensional object.

[0045] In the same layer of first embossed hologram 30 there is a secondembossed hologram, whose embossed structure 50 is again shown only in anextremely schematic representation in the form of lines. A possibleembodiment again comprises a diffraction grating similar to diffractiongrating 30. However, the spacing of the individual grating stripes isdifferent, so that a different wavelength interferes in this diffractiongrating compared to the first embossed hologram. Second embossedhologram 50 reconstructs in a different direction, which isschematically indicated by the different direction of hatching in FIG.2. It is of course also true of second embossed hologram 50 that anyother holographic information can be stored, e.g. the three-dimensionalholographic image of an object.

[0046] The external form of second embossed hologram 50 shows the number“123” in the shown example.

[0047]FIG. 3 shows an embodiment in which second embossed hologram 51,again indicated extremely schematically only as hatching, has gaps inthe form of digits. In gaps 31 first embossed hologram 30 becomesvisible. Thus, the digits of the number “123” shown by way of exampleare bordered by second embossed hologram 51.

[0048]FIG. 4 shows the embossing die of an inventive embodiment of anumbering embosser. Embossing die 7 is shown for structure 9, the digit“1” here. On embossing side 13 the digit “1” is formed in raised fashionin a laterally reversed representation. On the embossing surface of theraised digit, embossing structure 11 for an embossed hologram is appliedas a nickel master. Here, too, the representation is of course indicatedextremely schematically only as hatching.

[0049] Inventive optical elements can be produced by an inventive methodas follows.

[0050] First, first embossed hologram 30 is formed in conventionalfashion in an embossable film, which either is formed completely as anembossing layer or comprises an embossing layer. For example, theembossing layer can be a thermal lacquer layer in which a hologram ishot stamped in known fashion. For this purpose the desired embossedhologram structure is embossed using a hot stamping die. This processcan be effected in mass production. For example, the first embossedhologram structure can be embossed on a larger film unit and cut later.

[0051] The thus produced film having first embossed hologram 30 in theembossing layer is supplied to a numbering tool suitable for embossingconsecutive numbers. This embossing tool is used to emboss a number intothe same embossing layer where first embossed hologram 30 is located andthus replaces the embossed structure of the first embossed hologram inthe external form of the embossing surface of the embossing die of thenumbering tool. Second embossed hologram 50, 51 is thus embossed intofirst embossed hologram structure 30 in the external form of the numbersof the numbering tool.

[0052] Various forms for the numbers are conceivable. For example, thenumbers of the second embossed hologram structure can represent a numberpositively, as shown in FIG. 2, or appear as a border in negative form,as e.g. in FIG. 3.

[0053]FIG. 4 shows e.g. embossing die 7 for a positive digit “1.” Thesecond embossed hologram structure is located e.g. as a nickel master onembossing surface 11 of an embossing die of the numbering tool. In analternative embodiment, a nickel band bearing the structure forembossing the second embossed hologram is placed around the number wheelof the numbering embosser. During embossing, the structure of the nickelband is molded into the embossing layer of the first embossed hologramusing the numbering tool, without the embossing surfaces of thenumbering wheel having to be structured themselves.

[0054]FIG. 5 shows further inventive security feature 3 which can beprovided on bank note 1. As shown in FIG. 1, the security featureaccording to this embodiment again comprises number 5, in the shownexample the number “123.”

[0055] The inventive security feature of this embodiment comprisesembossed hologram 63, which is again shown only schematically in theform of lines. Said embossed hologram can also be a diffraction gratingwhose grating spacing is typically a few hundred nanometers to permitinterference effects of visible light to be produced in known fashion.The embossed hologram is of course not limited to such stripe-shapedholograms here either but can have any desired forms of embossedhologram that represent different information holographically, e.g. theimage of a three-dimensional object.

[0056] Within the outlines of embossed hologram 63 there are areas 61that do not bear any embossed structure like surrounding embossedhologram 63. This can be obtained by different proceduress, which aredescribed below.

[0057] In areas 61 there is no holographic reconstruction uponillumination, so that the holographic effect is left out in said areas.Total security feature 3 thus shows a holographic effect, e.g. therepresentation of a three-dimensional object. Only partial areas 61 inthe external form of the number “123” fail to reconstruct an imageholographically, so that they are recognizable and the information oftheir external form is visible.

[0058] Such an inventive optical feature can be produced as follows.Embossed hologram 63 is formed in conventional fashion in an embossablefilm, which either is formed completely as an embossing film orcomprises an embossing layer. The embossing layer can e.g. be a thermallacquer layer in which a hologram is hot stamped in known fashion. Forthis purpose the desired embossed hologram structure is embossed using ahot stamping die in this embodiment as well. This process can beeffected in mass production, e.g. embossed on a larger film unit and cutlater.

[0059] A laser printer or jet printer, similar to an ink jet printer, isused to apply printing lacquer 61 to embossed hologram structure 63 inthe desired external form, here the number “123,” thereby filling therelief of the embossed hologram structure. This is visible in crosssection in FIG. 6. In the areas filled with lacquer 61, embossedhologram layer 63 no longer reconstructs holographically whenilluminated with reconstruction light.

[0060] In another inventive method, printing lacquer 61 is applied to anembossable film in a desired external form, e.g. in the shape of thenumber “123,” with a laser printer or jet printer, similar to an ink jetprinter, before the embossed hologram is embossed. After a curing stepfor the printing lacquer, the film thus provided partly with printinglacquer is embossed in the way known for embossed holograms, therebyproducing embossed hologram 63. In the areas printed with lacquer 61,embossing is prevented during the embossing step so that here, too,there can be no holographic reconstruction in the completed opticalelement.

[0061] In all described embodiments, a hot-melt adhesive layer forfastening the optical element to document of value 1 is applied to theback of optical element 3 only after all necessary embossing processeshave been performed. Since said adhesive layer is applied only after allembossing processes, it cannot disturb the prior method steps.

[0062] In all inventive embodiments, the embossable substrate surfaceused can be a hot stamping foil, sticker embossing film, paper coatedwith thermal lacquer or substrate surface coated with UV lacquer. Theinvention is not limited to single number 5. The method and opticalfeatures are especially advantageous when the external form ofholographic area 50, 31 reconstructing differently or area 61 notreconstructing holographically at all is a consecutive number that isallotted individually to each optical element. This makes it possible toindividualize the particular optical element, e.g. in the manner of aregistration number for a document of value.

1. A method for producing an optical element, preferably a securityfeature, having the following steps: a¹) providing an embossable film orsubstrate surface having a first embossed hologram (30, 31) in anembossing layer, and b¹) embossing at least a second embossed hologram(50, 51) into the same embossing layer such that the first embossedhologram (30, 31) is partly replaced with the second embossed hologram(50, 51).
 2. A method according to claim 1, wherein the optical element(3) is individualized with step b¹).
 3. A method according to claim 2,wherein step b¹) is performed with an individualized embossing die.
 4. Amethod according to claim 1, wherein the first embossed hologram (30,31) and the second embossed hologram (50, 51) have differentreconstruction angles and/or different reconstruction wavelengths.
 5. Amethod according to claim 1, wherein step b¹) is performed using anembossing tool having at least one embossing surface (11) in the form ofthe desired external form of the second embossed hologram (50, 51).
 6. Amethod according to claim 5, wherein step b¹) comprises the embossing ofa second embossed hologram with the external form of an individualnumber.
 7. A method according to claim 6, wherein step b¹) comprises theuse of a numbering embosser whose embossing dies (7) comprise positiveor negative numbers (9) to which a holographic relief (11) is applied.8. A method according to claim 7, wherein the positive or negativenumbers (9) comprise metallic numbers produced by etching or engravingtechnology.
 9. A method according to claim 7, wherein a nickel master isused as a holographic relief (11).
 10. A method according to claim 6,wherein for performing step b¹) a nickel band having a holographicrelief is placed over the numbers of a number wheel of an embossednumbering unit.
 11. A method for producing an optical element,preferably a security feature, having the following steps: a²) printingpartial areas of an embossable film or substrate surface with a curableprinting lacquer (61), curing the printing lacquer, and b²) embossing anembossed hologram (63) on the printed substrate, the cured printinglacquer (61) preventing embossing in the printed partial areas.
 12. Amethod according to claim 1, having the following additional step: c)metalizing or coating with a highly refractive material on the embossedside of the optical element (3).
 13. A method for producing an opticalelement, preferably a security feature, having the following steps: a³)providing an embossable film or substrate surface having an embossedhologram (63) in an embossing layer, b³) applying a printing lacquer(61) in partial areas of the embossed hologram structure (63) such thatthe relief structure of the embossed hologram structure (63) is filledwith printing lacquer (61) in the partial areas, and c³) metalizing orcoating with a highly refractive material on the embossed side of theoptical element.
 14. A method according to claim 11, wherein in step b²)the printing lacquer (61) is applied in an external form representinginformation.
 15. A method according to claim 11, wherein step b²) isperformed for individualizing the optical element.
 16. A methodaccording to claim 15, wherein in step b²) the printing lacquer (61) isapplied in an external form having an individual external form forsingle optical elements (3).
 17. A method according to claim 16, whereinthe external form comprises the form of an individual number (5).
 18. Amethod according to claim 11, wherein the printing lacquer (61) isapplied with the desired external form with a jet printer or laserprinter.
 19. A method according to claim 11, wherein the printinglacquer (61) is transparent or colored-transparent.
 20. A methodaccording to claim 19, wherein after step b¹), an adhesive coating isapplied to the unembossed side of the film.
 21. A method according toclaim 1, wherein in step a¹), embossable substrate surfaces, inparticular hot stamping foils, sticker embossing films, paper coatedwith thermal lacquer or substrate surfaces coated with UV lacquer, areused.
 22. A numbering embosser for use in a method according to claim 1whose embossing surfaces are each provided with a holographic relief(11), the external form of the embossing surfaces corresponding eitherpositively or negatively to the external form of the number to beembossed.
 23. An optical element comprising a security feature fordocuments of value, that is produced by a method according to claim 1,having a first embossed hologram (30, 31) in an embossing layer and asecond embossed hologram (50, 51) in the same embossing layer, thesecond embossed hologram being disposed within the external outlines ofthe first embossed hologram.
 24. An optical element according to claim23, wherein the first embossed hologram (30, 31) and the second embossedhologram (50, 51) have different reconstruction angles and/or differentreconstruction wavelengths.
 25. An optical element according to claim23, wherein the second embossed hologram (50, 51) comprises anindividual external form, in particular the form of a number (5) eitherin positive or in negative representation.
 26. An optical elementcomprising a security feature for documents of value, having an embossedhologram structure (63) in an embossing layer and at least one partialarea (61) in the embossing layer in which the embossed relief is filled.27. An optical element comprising a security feature for documents ofvalue, having an embossed hologram (63) in an embossing layer and atleast one partial area (61) in the embossing layer in which the reliefof the embossed hologram structure is left out.
 28. An optical elementaccording to claim 26, wherein the at least one partial area (61)comprises an individual external form, in particular the form of anumber either in positive or negative representation.
 29. An opticalelement according to claim 23, wherein the film is provided with anadhesive layer on the unembossed side.
 30. A document of value having anoptical element according to claim
 23. 31. A document of value having anoptical feature produced by a method according to claim 1.